CYTHERE. 153 



16. Cythere Cluth^e, nov. sp. Plate XIII, figs. 16, 17. 



Shell, as seen from the side, subquadrate, highest in front, greatest height equal to 

 nearly two thirds of the length ; anterior extremity broad and well rounded, posterior 

 narrow and obliquely rounded ; superior margin almost straight, sloping from before 

 backwards, inferior deeply sinuated in the middle ; seen from above the outline is oblong, 

 subrectangular, with parallel, irregularly sinuous sides, suddenly tapered off towards the 

 front, which is truncated ; posterior extremity irregularly rounded. Shell-surface irregu- 

 larly mamillated, closely set with small subrotund pittings ; within the ventral margin runs 

 a broad rounded ridge, while the anterior half of the valve is occupied chiefly by one, the 

 posterior half by two, large rounded tubercles. 

 Length yg-th of an inch. 



Distribution. — Fossil. — Scotland : Cumbrae, Cartsdyke, Govan, Lag Arran. 



17. Cythere Finmarchica (G. 0. Sars). Plate X, figs. 18—21. 



1865. Cythereis Finmarchica, (Sars. Oversigt. Norges mar. Ostr., p. 41. 

 1868. Cythere — Brady. Monog. Rec. Brit. Ostrac, p. 410, pi. xxxi, 



figs. 9—13. 



Carapace of the female, as seen from the side, oblong, quadrangular, higher in front 

 than behind, greatest height equal to about half the length ; anterior extremity rounded ; 

 posterior subtruncate, somewhat angulated in the middle and usually divided into four 

 or five blunt teeth below. Superior margin sloping almost in a straight line from before 

 backwards ; inferior gently sinuated in the middle ; seen from above ovate, with sub- 

 parallel sides and obtuse extremities ; width scarcely equalling the height. Surface of 

 the shell marked wdth vaguely defined rounded pittings, and often with a median trans- 

 verse sulcus, in front of which is a large rounded tubercle bearing numerous (9 to 12) 

 irregularly disposed muscle-spots. Shell of the male narrower and more elongated. 

 Length -^^ih of an inch. 



Nearly allied to Cythere tuberculata, from which it differs, however, in having the 

 anterior margin entire or at most only slightly crenated, and in the character of the 

 posterior teeth, which are marginal crenulations rather than true spines ; the posterior 

 portion of the shell is also much less tumid than in the larger species, and there is only 



07ie large central tubercle. 



20 



